Fossil record '',
Latah Formation, North America The genus has an extensive fossil record, with numerous, distinctive species. Undisputed fossilized seeds have been found in
Cenozoic strata starting from the
Eocene throughout Europe, China and North America (though the genus became extinct in North America prior to the
Pleistocene). The oldest known fossils attributed to the genus are of leaves from
Cretaceous Alaska, referred to the species,
T. borealis.
Taxonomy Trapa natans is the
type species of its genus, named by the Swedish botanist
Carl Linnaeus in his
Species Plantarum in 1753. There are eight named varieties of
T. natans. "
T. bicornis" was described by the Swedish botanist
Pehr Osbeck as a species in 1757, but is treated as a synonym of
T. natans var
bispinosa.
T. rossica was described by the Russian botanist Viktor Nikolayevich Vassiljev and published by
Vladimir Leontyevich Komarov in 1949; it is treated as a synonym for
T. natans var
natans. File:Roman caltrop.jpg|The
generic name is derived from a Latin word for a
caltrop. File:Fruit of Trapa natans (water caltrop or water chestnut).jpg|
Trapa natans,4-horned fruit File:Trapa bicornis 1.jpg|
Trapa natans var
bispinosa,2-horned fruit
Subtaxa The following varieties are accepted: •
Trapa natans var.
africana – Tanzania, Uganda •
Trapa natans var.
bispinosa – Tropical and southern Africa, Indian Subcontinent, eastern Asia •
Trapa natans var.
japonica – Korea, Japan •
Trapa natans var.
magnicorona – Russian Far East, eastern China, Korea, Japan •
Trapa natans var.
natans – North Africa, Eurasia, and introduced to eastern North America •
Trapa natans var.
pseudincisa – Russian Far East, eastern China, Korea, Japan •
Trapa natans var.
quadricaudata – Cameroon,
KwaZulu-Natal, Southeast Asia, eastern China, Russian Far East, Japan •
Trapa natans var.
quadrispinosa – Himalayas to Japan == Distribution and habitat ==